(Re)assessment of the COSMED Quark CPET and VO2 Master Pro systems (2025)

Validation of metabolic-cart gas-exchange systems against simulator and Douglas-bag reference. Mean percent error for VO2 around 3.5% for the COSMED Quark and around 0.6% for the portable VO2 Master, with Douglas-bag error varying by intensity level (approximately -2% to -3% at moderate-to-high flows, reaching -3.7% at one extreme and +1.5% at another). Establishes that even gold-standard laboratory measurement carries a few per cent error. Strong.